Four charges equal to $-Q$ are placed at the four corners of a square and a charge $q$ is at its centre. If the system is in equilibrium, the value of $q$ is

  • A

    $-(Q/ 4)(1+ 2\sqrt 2)$

  • B

    $(Q/ 4)(1+ 2\sqrt 2)$

  • C

    $-(Q/ 2)(1+ 2\sqrt 2)$

  • D

    $(Q/ 2)(1+ 2\sqrt 2)$

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